1. Field of the Invention
This invention relates to a camera having a mirror box integrally molded with a focusing-screen mounting part and a pentagonal-prism mounting part.
2. Description of the Related Art
Heretofore, the pentagonal prism and the focusing screen of a single-lens reflex camera have been mounted in a manner as shown in FIG. 4. As shown, the camera is provided with a pentagonal-prism mounting member 17, which is mounted on a mirror box 4. The pentagonal-prism mounting member 17 includes a focusing-screen mounting part 17a, mirror-box mounting parts 17b and 17c and a pentagonal-prism mounting part 17e. The focusing-screen mounting part 17a and the pentagonal-prism mounting part 17e are arranged in parallel to each other. The pentagonal-prism mounting member 17 is provided further with an aperture 17d for guiding a reflected light flux coming from a mirror 6 to a pentagonal prism 7.
Referring again to FIG. 4, a focusing screen 1 is urged to move upward, as viewed in the FIGURE, by a leaf spring 19. The focusing screen 1 is thus caused to be abutting on the focusing-screen mounting part 17a of the pentagonal-prism mounting part 17 throughout the periphery thereof. A focusing-screen frame 18 is arranged to hold the focusing screen 1 and the leaf spring 19. The focusing screen 1, the leaf spring 19 and the focusing-screen frame 18 jointly form a focusing screen unit. The focusing-screen frame 18 is provided with projections 18a and 18b, which are arranged to engage and to be held by a focusing-screen mounting hole 4c which is formed in the mirror box 4 and a focusing-screen holding spring 20 which is secured to the mirror box 4. The focusing screen unit is arranged to be mountable and demountable by engaging and disengaging the focusing-screen holding spring 20 with and from the projection 18b. In other words, the focusing screen 1 and the pentagonal prism 7 are mounted on the pentagonal-prism mounting member 17 in parallel to each other. Further, the arrangement to have the focusing screen 1 abutting on the focusing-screen mounting part 17a throughout its periphery effectively prevents the intrusion of dust from coming from the inside of the mirror box 4.
However, the camera which is arranged in this manner has the mirror box 4 formed by aluminum or zinc die casting. Although the mirror box 4 formed in this manner is strong, it necessitates a secondary machining process which increases the cost. Besides, it is heavy. Further, since the pentagonal-prism holding member of the camera is discretely arranged, the conventional arrangement increases not only the number of parts but also the number of assembly work processes.